This invention relates to a machine for sharpening circular saw blades, and in particular to such a machine that simultaneously sharpens both sides of the saw blade.
Emter U.S. Pat. No. 4,823,649, Emter U.S. Pat. No. 4,846,023 and Emter U.S. Pat. No. 4,901,604 all disclose saw blade grinders which automatically advance a multiple-tooth circular saw blade one tooth at a time, index each tooth relative to a pair of side grinding wheels, clamp the blade against side-to-side movement and then sharpen the tooth. In these machines advancing and clamping are accomplished with pneumatic piston cylinders. Because of air flow dynamics, the speed at which pneumatic piston cylinders operate varies over time. Thus, individual flow control valves must be provided to achieve the proper timing between the clamping cylinder and the blade rotation cylinder. These flow control valves must constantly be adjusted to maintain the timing, which complicates operation of the machine and necessitates utilizing an operator with a higher skill level than otherwise would be required. The timing problems are made worse by the fact that blade sharpening machines operate at different speeds, depending on saw size, tip material and sharpening requirements. Each time machine speed is changed the pneumatic cylinder flow valves must be readjusted to obtain correct timing between saw blade rotation and clamping, which reduces productivity.
The subject invention overcomes the foregoing shortcomings and limitations of prior automatic dual side saw grinders by utilizing the same actuator for advancing the saw blade and for operating the blade clamping mechanism. Having only one piston cylinder eliminates timing problems and thus the need for flow control valves. In a preferred embodiment, this is accomplished with a double acting two-ended pneumatic piston cylinder. The piston cylinder is mounted similar to the clamping cylinder in the prior art machines with one side of the clamping mechanism being attached to the piston at one end of the piston cylinder. The other end of the piston cylinder engages a push-pull cable that is attached to a rocker bar/crankshaft linkage that converts the linear movement of the cable into rotational movement of the spindle that carries the saw blade. The linkage is adjustable to vary the crankshaft stroke in order to accommodate saw blades with different tooth spacing. The saw blade is coupled to the spindle through a magnetic clutch which permits the piston cylinder to be operated when the saw blade is restrained against rotation.
In operation, a tooth on the saw blade is advanced to the grinding position by moving the piston cylinder in the direction that causes the cable to be extended. This simultaneously releases the clamping mechanism so that the blade is free to rotate. The linkage and cable are arranged so that extension of the piston cylinder advances the blade farther than is necessary, and the tooth is placed in the proper position by moving the piston cylinder in the opposite direction until the tooth contacts an indexing stop. The piston cylinder continues to move in the opposite direction until the clamp is reengaged and the grinding operation is then performed. The foregoing sequence is repeated after each tooth is sharpened until sharpening of the blade is completed.
Operation of the piston cylinder is accomplished by an air valve that is located in the piston cylinder pneumatic lines. The air valve is actuated through a cam that is operated by the motor that advances the grinding wheels. Thus, blade advancement, clamping and grinding are synchronized and are automatically sequenced.
Accordingly, it is a primary object of the subject invention to provide an automatic dual side saw blade grinder in which the saw blade advancement mechanism and clamping mechanism are actuated through a common actuator.
It is a further object of the subject invention to provide such a grinder which is fully automatic and requires no timing adjustment to synchronize the advancement and clamping mechanisms.
It is a still further object of the subject invention to provide such a grinder in which the operating speed of the grinder can be altered without upsetting this synchronization.
It is a yet further object of the subject invention to provide a method for automatic dual side grinding of saw blades without the necessity of adjusting the relative timing of the blade advancement and clamping mechanisms.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.